1. Technical Field
This disclosure relates to a laser system and a laser light generation method.
2. Related Art
Typical excimer lasers as ultraviolet light sources for use in semiconductor lithography are KrF excimer lasers whose output wavelength is approximately 248 nm and ArF excimer lasers whose output wavelength is approximately 193 nm.
Most of the ArF excimer lasers are marketed as two-stage laser systems including an oscillator stage laser and an amplifier stage. Common major components of the oscillator stage laser and the amplifier stage in two-stage ArF excimer laser systems include the following. The oscillator stage laser includes a first chamber, while the amplifier stage includes a second chamber. The first and second chambers contain laser gas (mixture gas of F2, Ar, Ne, and Xe) sealed therein. The oscillator stage laser and the amplifier stage are provided with a power supply for supplying electric energy for exciting the laser gas. The oscillator stage laser and the amplifier stage may have separate power supplies or share a common power supply. Inside the first chamber, first discharge electrodes including a first anode and a first cathode that are connected to the power supply are provided. In a similar manner, second discharge electrodes including a second anode and a second cathode that are connected to the power supply are provided inside the second chamber.
The specific features of the oscillator stage laser include, for example, a line narrowing module. The line narrowing module typically includes a grating and at least one prism beam expander. A semitransparent mirror and the grating constitute an optical resonator. The first chamber of the oscillator stage laser is arranged between the semitransparent mirror and the grating.
When an electric discharge occurs between the first anode and the first cathode of the first discharge electrodes, the laser gas is excited, to thereby emitting light upon releasing the excitation energy. The light is then subjected to wavelength selection by the line narrowing module and the resulting light is output as laser light from the oscillator stage laser.
A two-stage laser system whose amplifier stage is a laser including a resonator is called a master oscillator/power oscillator (MOPO), while a two-stage laser system whose amplifier stage is not a laser without a resonator is called a master oscillator/power amplifier (MOPA). When laser light from the oscillator stage laser is present in the second chamber of the amplifier stage, control is performed so that an electric discharge occurs between the second anode and the second cathode of the second discharge electrodes. As a result, the laser gas in the second chamber is excited, the laser light is amplified, and the resulting light is output from the amplifier stage.